1. Field of the Invention
The present invention relates to a voltage limiting regulator. More particularly, the invention comprises a voltage limiting regulator for use cooperatively with an alternator having split, DC-excited fields and wherein the voltage output from the alternator may be controlled by varying the DC-excitation voltage provided to the field windings.
The need for portable, compact, high-power AC electric power generators is widely felt. Not only are such devices useful for powering the tools in the field away from normal AC supply mains, they are particularly useful for providing emergency power during time that AC power is unavailable from the power grid. Vehicle-mounted AC generators have proven to be particularly useful because of the ease with which they may be transported to a job site or other location in need of locally-generated, AC power.
2. Description of the Prior Art
U.S. Pat. No. 3982,173 for AC-DC VOLTAGE REGULATOR, issued Sep. 21, 1976 to Clyde Raymond Berry, et al. teaches an AC-to-DC convertor employing a rectifier and a crowbar type voltage regulator. A control voltage is developed and fed back to a current-controlled switch which functions to maintain a constant output voltage from the converter under varying loads.
In contradistinction, the inventive regulator is designed for use with an alternator producing a single-phase AC output voltage and using DC excitation of its field windings. The applied DC excitation voltage may be varied thereby varying the AC output voltage from the alternator. The voltage limiting regulator circuit senses a changing AC output voltage and responds by changing the DC excitation voltage thereby maintaining a substantially constant AC output voltage under a varying load.
U.S. Pat. No. 4,800,291 for ELECTRONIC CIRCUIT FOR CONTROL OF A VOLTAGE REGULATOR OF AN ELECTRICAL GENERATOR, issued Jan. 24, 1989 to Jack K. Bowers discloses an apparatus for synchronizing the voltage and phase of an AC generator to an existing power grid. Unlike the voltage-limiting regulator of the instant invention, BOWERS uses sophisticated electronic circuitry to accomplish the synchronization function. The inventive regulator, on the other hand, is intended for application with stand-alone AC generators, each driving a varying load. The phase of each individual generator is essentially constant. Consequently, there is no need to match its phase to that of any other generator. The output voltage of a generator using the inventive regulator is controlled as the load applied to the generator changes.
U.S. Pat. No. 5,617,011 for METHOD AND SYSTEM FOR LIMITING GENERATOR FIELD VOLTAGE IN THE EVENT OF REGULATOR FAILURE, issued Apr. 1, 1997 to Kathleen M. Hammer, et al. teaches a circuit for limiting the field voltage provided a generator in the event of a field coil short circuit or regulator failure. Nothing in HAMMER, et al. teaches the regulation of an AC generator""s output voltage using a rectified feedback signal, a comparitor and an output stage to directly provide a varying DC field energization voltage to the generator.
U.S. Pat. No. 5,656,922 for VEHICLE BASED AC POWER SYSTEM, issued Aug. 12, 1997 to William J. LaVelle, et al. teaches a hybrid AC generator utilizing both permanent magnets and DC-driven coils for field generation. The field coils may be arranged in switchable buck or boost modes to control the alternator output, thereby preventing an overvoltage output. The LaVELLE, et al. apparatus allows designing a vehicle-mounted alternator capable of full output at any range of engine speeds, from idle to full throttle.
The inventive regulator, on the other hand, is designed to provide a continuously varying DC voltage for excitation of the field windings of a conventional (i.e., not a hybrid) alternator whereby the AC output voltage is maintained substantially constant under varying load conditions.
U.S. Pat. No. 5,675,237 for OUTPUT CONTROL DEVICE FOR VEHICLE AC GENERATOR, issued Oct. 7, 1997 to Shiro Iwatani discloses a switching arrangement which allows utilization of a single alternator for selectively charging a vehicle""s battery and providing a high-voltage AC output for powering an external load. Unlike the inventive regulator, there is no teaching of a voltage regulation function based upon changing the DC voltage applied to the alternator for field excitation.
U.S. Pat. No. 5,686,819 for CONTROL APPARATUS FOR AC GENERATOR OF MOTOR VEHICLES, issued Nov. 11, 1997 to Shiro Iwatani, et al. also teaches a switching arrangement for directing alternator output to a vehicle battery or, in a second mode of operation, to an external AC load. There is still no teaching of a voltage regulation function based upon changing the DC voltage applied to the alternator for field excitation.
None of the above inventions and patents, taken either singly or in combination, is, however, seen to anticipate or suggest the instant invention as claimed.
The present invention relates to a voltage-limiting regulator for use with an AC generator having DC-excited fields. The AC output voltage from the generator is sensed and compared to a fixed reference voltage. An algebraic difference voltage, representative of the sensed difference, is amplified and applied to the DC field excitation input of the AC generator. As load changes, the AC output voltage from the generator varies. By sampling the generator""s AC output voltage, a feedback voltage is developed which is supplied to the generator""s field windings. In this way the AC output voltage is held constant under varying load conditions. The voltage-limiting regulator is particularly useful for vehicle-mounted, high power, single phase AC generators.
Accordingly, it is a principal object of the invention to provide a voltage-limiting regulator for use with an AC generator having DC-excited fields.
It is another object of the invention to provide a voltage-limiting regulator for use with an AC generator having DC-excited fields which provides a substantially constant generator output under varying load conditions.
It is a further object of the invention to provide a voltage-limiting regulator for use with an AC generator having DC-excited fields which provides a substantially constant generator output under varying load conditions by changing a DC excitation voltage supplied to the field-generating mechanism.
Still another object of the invention is to provide a voltage-limiting regulator for use with an AC generator having DC-excited fields which uses a comparitor to provide a feedback voltage which is derived from the algebraic comparison of the instantaneous AC output voltage from the AC generator and a fixed, predetermined reference voltage.
An additional object of the invention is to provide a voltage-limiting regulator for use with an AC generator having DC-excited fields which allows the construction of high-power, single phase AC generators which are capable of maintaining essentially constant output voltage under varying load conditions.
It is again an object of the invention to provide a voltage-limiting regulator for use with an AC generator having DC-excited fields which allows the construction of high-power, single phase AC generators which are suitable for mounting on a motor vehicles.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.